Common to most operating BWR's, the core spray cooling water is delivered to the reactor core region by piping internal to the reactor vessel. The core spray piping systems in operating BWR's are of welded construction. The welds in the original core spray system piping are susceptible to Intergranular Stress Corrosion Cracking (IGSCC).
The lower portion of BWR's internal core spray piping is commonly referred to as the “downcomer piping”. There are a total of four vertical downcomer pipes, which supply cooling water to sparger piping interior to the shroud 14. Two of these downcomer pipes 10 located on one side of the shroud 14 are shown in FIG. 1. Each of the downcomer pipes 10 consists of two separate vertical piping segments 16 and 18, which are joined together at the time of reactor vessel assembly by a slip joint coupling 20, as shown in cross-sectional view in FIG. 2. The lower segment 18 of the downcomer 10 incorporates a receptacle 22, which is welded in the shop to the lower vertical segment 18 of piping by virtue of a P7 weld. During reactor vessel assembly, the upper piping segment 16 of the downcomer is trimmed in length to mate with the lower segment 18. A sleeve 24, which slides on the upper downcomer piping segment 16 is then inserted into the receptacle 22, thereby covering a joint 26 between the upper and lower piping segments 16 and 18. Circumferential fillet welds, P5 and P6, are then applied to seal the slip joint 26 with the upper downcomer piping segment 16 and receptacle 22, respectively. It is worthy to note that even though separate downcomer pipes may penetrate the shroud 14 at different elevations, typically, the slip joint couplings 20 are all located at the same elevation in a reactor vessel 12.
In the event that cracking should occur in any one of the three slip joint coupling welds P5, P6 and/or P7, the structural integrity of the downcomer slip joint coupling 20 would be lost. A preemptive repair would be to install a clamping device, which would prevent separation of the downcomer slip joint coupling in the event that circumferential through-wall cracking should occur. The present invention is directed to a remotely installed repair device, which structurally replaces cracked welded joints in the core spray downcomer slip joint coupling.